1. Field of the Invention
The present invention generally relates to transmission and presentation of broadcast digital video and audio program content and, more particularly, to protection of such data stored in a set-top box (STB) or mass storage device connectable thereto from unauthorized access.
2. Description of the Prior Art
Since its invention, television has been recognized to have great economic and social potential. At the present time, when wide bandwidth transmission systems such as coaxial cable systems are becoming relatively ubiquitous, much of the economic and social potential derives from the variety of programming or other information which can be provided to users and the willingness of users to pay for access to particular information, such as pay-per-view movies at a time convenient to them.
While coaxial cable distribution systems provide very substantial numbers of choices of information available as well as some capacity for so-called upstream signalling and even Internet communications of increased speed relative to telephone/modem arrangements, there is increased demand for wider variety and flexibility of programming which can only be provided, at the present state of the art, through digital communications using extremely broad band transmission media such as microwave, satellite and fiber optic links.
Even with these broad band communication media, the required capacity, the volume and variety of data contained in common programming requires extreme compression to support the number of separate communications which may be required to be transmitted over a communication link of finite although substantial capacity. Accordingly, a compression convention referred to as MPEG (Motion Picture Experts Group has been promulgated in several versions (e.g. MPEG-2) and has become an industry standard. This standard is extremely flexible and adaptive to transmission content to allow extreme compression and is largely compatible with error recovery and hiding arrangements which support acceptable video and audio playback even though the digital transmission medium is considered “lossy” and reception of data with missing or corrupted segments or packets is a common occurrence.
In order to implement this compression convention and recover decompressed data after transmission, a so-called “set-top box” (STB) has been developed and, at the current time, has a well-established architecture. The processing of which the STB is capable is, of course, very substantial since MPEG compression or any other type of digital video transmission must be very complex and must be performed reliably within a short period of time in order to present a potentially changing display without interruption. Generally, very little storage is provided for the audio and/or video signal in a STB for the simple reason that the signal usually must be used for display within a very short time after receipt.
However, public familiarity with the functions of video cassette recorders (VCRs) is increasingly leading to a demand for substantial storage to be provided within the STB and for further storage on an outboard mass storage device such as a hard disk drive or compact disk recorder/playback device together with user controls over playback and recording similar to those provided by VCRs. The MPEG STB architecture provides for such storage in an encoded and compressed digital form to limit the data storage capacity required with decompression and decoding upon playback. Storage in digital form also allows such storage to be performed with no increased loss of video or audio fidelity.
Additionally, user demand for specialized features and image enhancement has required substantially increased complexity beyond the demands of MPEG processing. For example, a separate microprocessor and substantial memory is generally included and dedicated to provide user-definable functions such as overlays, picture-in-picture displays, graphics overlays and other image manipulations. This additional hardware complexity has pushed the cost of the STB close to the limit of consumer acceptance and economic viability. Therefore, additional functions may only be included if they can be implemented very economically with little additional hardware and without use of the additional dedicated microprocessor.
To protect the value of data distributed over such a system, it is desired to protect selected data from unauthorized access. This is generally done at the current state of the art by encryption of the data. This encryption requires considerable data manipulation under severe and critical time constraints as well as additional storage and secure handling of encryption keys that must be shared between devices when data is sourced from one device and played back on another as would generally be the case when the data is transmitted in encrypted form and decrypted and played back on another device such as a STB corresponding to an authorized access. This is also the case where an unauthorized recording could be made from an authorized STB that would generally be created for the purpose of playback on another STB or other apparatus. Accordingly, data recorded in or through a STB must be recorded in an encrypted form and decrypted during playback; increasing the processing burden to present the data (especially video) in the appropriate original time sequence.
At the present state of the art, no arrangement or technique has been suggested for providing encrypted storage with a reduced number of keys that reduces storage space and data manipulation requirements and remains effective to prevent unauthorized duplication of data from the STB. In this regard, copying of data as recorded in or through the STB can be rapidly performed relative to copying the decoded and decrypted audio and video signals on, for example, a video cassette recorder (VCR). (While some forms of copy protection exist to prevent copying of video programming on VCRs, no similar protection exists against copying the “clean” (although encoded and compressed) digital signals present at the level of STB storage.) Further, the digital storage of the STB allows rapid storage of multiple generations of copies of identical quality. Therefore, prevention of copying from a STB for playback on another STB or other device of similar functionality (e.g. a suitably programmed personal computer) is of substantially greater importance than preventing dubbing of video cassettes.